Aceria cephalonea, Sycamore Gall Mite

Common Name: Sycamore Gall Mite

Appears as lots of small red lumps (galls) which are about the size of a pinhead on the upper surface of young leaves, giving the appearance of a rash of pimples. The galls are caused by tiny mites (less than 0.2mm long). The immature and adult mites emerge in the spring after overwintering in bark crevices and other tiny spaces. As they pierce individual cells to feed on the plant tissue the surrounding cells are prompted to divide, therefore enlarging and forming the gall. By mid-May the mites start to lay eggs within the galls and several generations can occur over a season. The adults leave the galls in autumn before leaf fall to overwinter.

Other than the affect to the appearance of the leaves, this pest does little lasting damage. It affects Sycamore trees (Acer pseudoplatanus), some ornamental acers and hedge maples (Acer campestre). More prevalent on young trees. The symptoms occur from April onwards.

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